I have seen random Forbidden or Permission Denied messages in the context of other, unrelated web-sites ... and it always appeared to, indeed, be “random.”   As far as I can tell, it seems to be something to do with proxy-servers or Other Arkane Mysteries™.   Certainly, the site owners and/or the gods need to be made aware that this is happening when it happens to any “noticeable” degree, but I do not believe that it should be construed as an intentional response of this (or any) site.   In other words, it isn’t anything that you did or didn’t do.